Tag: CD146

Johns Hopkins University medical researchers have reported the derivation of human induced-pluripotent stem cells (iPSCs) that can repair damaged retinal vascular tissue in mice. These stem cells, which were derived from human umbilical cord-blood cells and reprogrammed into an embryonic-like state, were derived without the conventional use of viruses, which can damage genes and initiate cancers. This safer method of growing the cells has drawn increased support among scientists, they say, and paves the way for a stem cell bank of cord-blood derived iPSCs to advance regenerative medical research.

In a report published Jan. 20 in the journal Circulation, Johns Hopkins University stem cell biologist Elias Zambidis and his colleagues described laboratory experiments with these non-viral, human retinal iPSCs, that were created generated using the virus-free method Zambidis first reported in 2011.

“We began with stem cells taken from cord-blood, which have fewer acquired mutations and little, if any, epigenetic memory, which cells accumulate as time goes on,” says Zambidis, associate professor of oncology and pediatrics at the Johns Hopkins Institute for Cell Engineering and the Kimmel Cancer Center. The scientists converted these cells to a status last experienced when they were part of six-day-old embryos.

Instead of using viruses to deliver a gene package to the cells to turn on processes that convert the cells back to stem cell states, Zambidis and his team used plasmids, which are rings of DNA that replicate briefly inside cells and then are degraded and disappear.

Next, the scientists identified and isolated high-quality, multipotent, vascular stem cells that resulted from the differentiation of these iPSC that can differentiate into the types of blood vessel-rich tissues that can repair retinas and other human tissues as well. They identified these cells by looking for cell surface proteins called CD31 and CD146. Zambidis says that they were able to create twice as many well-functioning vascular stem cells as compared with iPSCs made with other methods, and, “more importantly these cells engrafted and integrated into functioning blood vessels in damaged mouse retina.”

Working with Gerard Lutty, Ph.D., and his team at Johns Hopkins’ Wilmer Eye Institute, Zambidis’ team injected these newly iPSC-derived vascular progenitors into mice with damaged retinas (the light-sensitive part of the eyeball). The cells were injected into the eye, the sinus cavity near the eye or into a tail vein. When Zamdibis and his colleagues took images of the mouse retinas, they found that the iPSC-derived vascular progenitors, regardless of injection location, engrafted and repaired blood vessel structures in the retina.

“The blood vessels enlarged like a balloon in each of the locations where the iPSCs engrafted,” says Zambidis. Their vascular progenitors made from cord blood-derived iPSCs compared very well with the ability of vascular progenitors derived from fibroblast-derived iPSCs to repair retinal damage.

Zambidis says that he has plans to conduct additional experiments in diabetic rats, whose conditions more closely resemble human vascular damage to the retina than the mouse model used for the current study, he says.

With mounting requests from other laboratories, Zambidis says he frequently shares his cord blood-derived iPSC with other scientists. “The popular belief that iPSCs therapies need to be specific to individual patients may not be the case,” says Zambidis. He points to recent success of partially matched bone marrow transplants in humans, shown to be as effective as fully matched transplants.

“Support is growing for building a large bank of iPSCs that scientists around the world can access,” says Zambidis, although large resources and intense quality-control would be needed for such a feat. However, Japanese scientists led by stem-cell pioneer Shinya Yamanaka are doing exactly that, he says, creating a bank of stem cells derived from cord-blood samples from Japanese blood banks.

The ability of endothelial progenitor cells or EPCs to repair skeletal muscle is well established, but the ability of these cells to repair a damaged heart is unknown. Johnny Huard from the McGowan Institute for Regenerative Medicine at the University of Pittsburgh and his group investigated the therapeutic capabilities of human blood vessel-derived EPCs that had been isolated from skeletal muscle to treat heart disease in mice.

When mice that had been given infusions of EPCs after a heart attack were compared with mice that had received a placebo, the EPC transplanted mice definitely fared much better. Echocardiographic studies of the hearts showed that EPC transplantation reduced enlargement of the left ventricle (the main pumping chamber of the heart), and also significantly improved the ability of the heart to contract.

In addition to comparing the ability of EPCs to improve the function of the heart after a heart attack with placebos, they were also compared to stem cells known to make skeletal muscle. These stem cells are called “CD56+ myogenic progenitor cells,” which is a mouthful. CD56+ myogenic progenitor cells or CD56+ MPCs can form skeletal muscle; and infusions of them can improve the structure of the heart after a heart attack and prevent it from deteriorating. However, transplanted EPCs were superior to CD56+ MPCs in their ability to heal the heart after a heart attack.

The transplanted EPCs were able to substantially reduced scarring in the heart, and significantly reduced inflammation in the heart. In fact, then the culture medium in which EPCs were grown was injected into mouse hearts after a heart attack, this medium also suppressed inflammation in the heart.

When Huard and his co-workers examined the genes made in the EPCs, they found that these stem cells cranked out proteins known to decrease inflammation (IL-6, LIF, COX-2 and HMOX-1 for those who are interested), especially when the cells were grown under low oxygen conditions. This is significant because in the heart after a heart attack, blood vessels have died off and the supply of blood to the heart is compromised. The fact that these cells are able to do this under these harsh conditions shows that they make exactly the most desirable molecules under these conditions.

The biggest boon for these cells came from examinations of blood vessel formation in the heart. Blood vessel production in the EPC-transplanted hearts was significantly increased. The EPCs formed a host of new blood vessels and extending “microvascular structures” or smaller supporting blood vessels and larger capillary networks too.

Once again, when grown under oxygen poor conditions, the EPCs jacked up their expression of pro-blood vessel-making molecules (VEGF-A, PDGF-β, TGF-β1 and their receptors). When EPCs were labeled with a green-glowing protein, fluorescence tracking showed that they actually fused with heart cells, although it must be emphasized that this was a minor event.

These pre-clinical studies show remarkable improvements in the heart after a heart attack, and they apparently induce these improvements through several different mechanisms. They make new structures and they secrete useful molecules. These significantly successful results should provide the basis for clinical trials with these cells.